AWH! I'm so sorry for you! I feel your pain - I've got the exact same stains on one of my bags... But that was just Sergio Castelli or Elio Fiorucci or something. It had stains all over it so I had to throw it away - I hated to do it, but that was a cheap bag. I'd totally freak out if something happened to an LV!
But if I were you, since it'sso expensive to replace the bottom, I'd just keep this one and use it for things like picknicks, going to the beach, stuff like that when your bag can get dirty, so you don't want to take a good one. And it's only on the bottom, so it will still look good!
I'd definitely save the money to buy an other bag you like a lot.